1. Field of the Invention
The present invention relates to an apparatus for controlling a heater for heating a window of an automobile so as to eliminate frost, snow, ice, and so forth.
2. Description of the Related Art
The above-described window heater controlling apparatus for an automobile is known from, e.g., Japanese Patent Publication No. 61-33735 (1986).
In this conventional window heater controlling apparatus as shown in FIG. 1, a heating resistor element 1 made of a metal powder using the vapor method is mounted on a window glass such as a windshield of an automobile (not shown in detail). While heating the window by this heater element 1, frost, snow and ice or the like are melted away.
More specifically, either when an ice-melting switch 2 is turned off, or after five minutes have passed since this switch 2 is turned on, a contact 3a of a control relay 3 is changed over in response to an energizing signal derived from a heater control unit 4 so that electronic connections are made between an output unit 6 of an alternator 5, a battery 7 having a rated voltage of 12 V, and other electric loads. Based upon the output voltage produced from the output unit 6 of the alternator 5, a voltage regulator 8 controls an energizing current supplied to a rotor coil 5a of the alternator 5 in such a manner that an output voltage applied to a stator coil 5b of the alternator 5 is set up to, for instance, 13.5 V when the battery voltage is lower than 12.5 V. That is, the regulator 8 performs the normal voltage control. It is so designed that the energizing current is furnished from the battery 7 via the control unit 4 and an ignition switch 9 to this voltage regulator 8.
To the contrary, when five minutes have not yet passed since the ice-melting switch 2 is turned on and also unless this switch 2 is turned off, the above-described normal voltage control is interrupted so as to execute the ice melting operation.
In other words, when a detection is made that a gear shift position sensor 10 detects that the gear shift position of the power transmission is at the neutral position (involving the parking position), namely an automobile is stopped, the control unit 4 performs the following control operations after interrupting the generation of the alternator 5. That is, an electronic fuel control unit 12 is under control such that the output voltage of the alternator 5 is increased up to 60 V, for example, in response to a detection voltage across a voltage detecting resistor 11. The electronic fuel control unit 12 controls a supply amount of a fuel to an engine of the automobile as follows. When the engine revolution is increased, the higher output voltage is produced from the alternator 5, whereby the higher output voltage can be matched with the power consumption of the above-described heater element 1.
The control unit 4 switches the contact 3a of the control relay 3 so as to connect the output unit 5a of the alternator 5 with the electric heater resistor 1. Thereafter, a maximum energizing current is supplied to the rotor coil 5a in order to commence the generation for the ice-melting operation.
Thus, the heater resistor 1 is energized to heat the resistor itself, whereby iced particles such as frost and snow attached to the window glass are melted away.
Reference numeral 13 indicates an ignition relay for supplying a power supply voltage to the control unit 4; reference numeral 14 indicates an indication lamp for ice-melting operation; and, reference numeral 15 is a charge lamp for indicating whether or not the alternator 5 generates the AC power.
In the above-described conventional heater controlling apparatus, after the control relay 3 is changed when the ice-melting operation is commenced, the power generation by the alternator is again performed by supplying the maximum energizing current to the rotor coil 5a of the alternator 5 in such a manner that the output voltage appearing the stator coil 5b becomes 60 V. As a result, the following problems may be caused.
Since the load current of the electric resistor 1 flows through the alternator 5 at the substantially same time as the power generation by the alternator 5 starts, a reaction torque is exerted in the alternator 5, by which the rotation of alternator 5 is stopped. In particular, the great reaction torque caused by the heavy electric load such as the electric resistor 1, is simultaneously produced when the heavy load current flows through the alternator 5. As a result, since the engine speed is lowered, or the engine power is considerably lowered, the idling operation is brought into an unstable condition which causes higher vibrations, or shocks due to changes in the driving torque. As a consequence, a comfortable driving cannot be achieved.